Printed circuit board to printed circuit board radio frequency interface

Abstract

A radio frequency (RF) coupler is configured to carry RF signals from a first printed circuit board (PCB) to a second PCB. The RF coupler includes a first trace on an outer surface of the first PCB and a second trace on an outer surface of the second PCB. The first trace and the second trace at least partially overlap to form an RF broadside coupler when the first PCB is positioned adjacent the second PCB. Each of the first trace and the second trace are covered by respective dielectric coatings such that a direct current (DC) electrical connection between the first trace and the second trace is prevented when the first PCB is positioned adjacent the second PCB.

1 . A radio frequency (RF) coupler configured to carry RF signals from a first printed circuit board to a second PCB, the RF coupler comprising:
 a first trace on an outer surface of the first PCB;   a second trace on an outer surface of the second PCB;   the first trace and the second trace at least partially overlapping to form an RF broadside coupler when the first PCB is positioned adjacent the second PCB; and   each of the first trace and the second trace being covered by respective dielectric coatings such that a direct current (DC) electrical connection between the first trace and the second trace is prevented when the first PCB is positioned adjacent the second PCB.   
     
     
         2 . The RF coupler  claim 2 , wherein the first PCB has a multi-layer structure including at least three metal layers and at least two dielectric layers, and wherein the first PCB further comprises:
 a first ground plane on the outer surface of the first PCB, the first ground plane defining a metal-free window surrounding the first trace; and   a second ground plane on a second metal layer of the first PCB, the second ground plane extending over the metal-free window of the first ground plane and being separated from the first trace by at least two of the dielectric layers of the first PCB.   
     
     
         3 . The RF coupler of  claim 2 , wherein the second metal layer of the first PCB is a second outer surface of first PCB. 
     
     
         4 . The RF coupler of  claim 2 , wherein the first PCB further comprises a plurality of vias connecting the first and second ground planes in a region surrounding the metal-free window of the first ground plane. 
     
     
         5 . The RF coupler of  claim 2 , wherein the first PCB further comprises at least one windowed ground plane on a metal layer between the first and second ground planes, the at least one windowed ground plane having a metal-free window that is coextensive with metal free window of the first ground plane. 
     
     
         6 . The RF coupler of  claim 5 , wherein the plurality of vias are further connected to the at least one windowed ground plane between the first and second ground planes. 
     
     
         7 . The RF coupler of  claim 1 , wherein the second PCB has a multi-layer structure including at least three metal layers and at least two dielectric layers, and wherein the second PCB further comprises:
 a third ground plane on the outer surface of the second PCB, the third ground plane defining a metal-free window surrounding the second trace; and   a fourth ground plane on a second metal layer of the second PCB, the fourth ground plane extending over the metal-free window of the third ground plane and being separated from the second trace by at least two of the dielectric layers of the second PCB.   
     
     
         8 . The RF coupler of  claim 7 , wherein the second metal layer of the second PCB is a second outer surface of second PCB. 
     
     
         9 . The RF coupler of  claim 7 , wherein the second PCB further comprises a plurality of vias connecting the third and fourth ground planes in a region surrounding the metal-free window of the third ground plane. 
     
     
         10 . The RF coupler of  claim 7 , wherein the second PCB further comprises at least one windowed ground plane on a metal layer between the third and fourth ground planes, the at least one windowed ground plane having a metal-free window that is coextensive with metal free window of the third ground plane. 
     
     
         11 . The RF coupler of  claim 10 , wherein the plurality of vias are further connected to the at least one windowed ground plane between the third and fourth ground planes. 
     
     
         12 . The RF coupler of  claim 1 , wherein a width of the first trace is selected based at least in part on a desired impedance of the RF broadside coupler. 
     
     
         13 . The RF coupler of  claim 1 , wherein, in an overlap area between the first trace and the second trace, a width of the second trace is less than the width of the first trace. 
     
     
         14 . The RF coupler of  claim 1 , wherein a difference between respective widths of the first and second traces determines a positioning tolerance of the first PCB and the second PCB. 
     
     
         15 . The RF coupler of  claim 1 , wherein a length of an overlap area between the first trace and the second trace is selected based on desired performance criteria of the RF broadside coupler. 
     
     
         16 . The RF coupler of  claim 15 , wherein the desired performance criteria of the RF broadside coupler comprises at least one of insertion loss and return loss over a frequency range of interest.